In fact, many studies have shown now that psychosocial issues are a key factor in patients who develop chronic pain. If you've had back pain for six months now, then you fall into the definition of someone who is having a problem with chronic pain.
When infection, tumor, or other more serious cause of back pain has been ruled out, it's a good idea to look more closely at the psychosocial piece of the puzzle. Many studies have shown now that the presence of anxiety and/or depression makes a difference.
Patients are less likely to respond to any kind of therapy or treatment if there was a high level of distress before treatment. This is true whether they have surgery, physical therapy, or some other form of treatment. Higher levels of distress actually predict greater pain and disability over the course of follow-up.
It sounds like you are in good hands if your PA knows this and is making an effort to explore all areas of possibility with you. It's probably not the case that he thinks this is all in your head. A good health care professional recognizes all factors (including psychologic and social) that can contribute to a problem.